Re: More FireLite debacles


"Don T" <-painter-@xxxxxxxxxx> wrote in message
news:CNsFe.4665$0C.4264@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> Lloyd,
>
> Have you looked for a "floating ground" fault? I say this based on your
> comment that the CD is on a different branch circuit than the audio amps.
>
Yes. That would have been a potential source of 60Hz AM in the time code
(but not likely, see below). More likely, it would superimpose 60Hz on the
music; you'd hear it coming out the amps. The output to the time code
equipment is not fed to or through the amps. The amps are on the same phase
as the CD, just not the same breaker. But there is no electrical ground,
only a signal ground between the CD player and the firing equipment. The
FireLite is used on internal battery power during a show, and only connected
to the AC charger between shows. There also exists no electrical ground
(common to the local power ground) for the firing network, only a signaling
ground and a "firing power" ground. The modules all derive their power from
the firing controller. The entire system - network and all - "floats" with
respect to the AC supply. But FWIW, I tried the system with the AC supply
connected, too. There is an AC neutral leg "ground" on the charger, but no
earth ground, and only 2-pin AC into the FireLite charging input. The wall
wart is a simple transformer, not a supply/regulator.

Besides, I saw no 60Hz noise on the time code line, only a random 2db
amplitude jitter that appeared to coincide with the music audio. 60Hz is
pretty easy to see and recognize, even at small levels. I didn't have the
time or equipment channels to do subtractive analysis of the noise itself,
to see if it matched the music waveforms. But it's a pretty good guess,
since the noise doesn't appear until the amp stack is up to about 3500 watts
of output.

BTW, that's one reason we used a low-impedance drive with equipment-end
impedance matching. But again here, we've also run the system on a 600 ohm
line-level output with _exactly_ the same results. And we've changed CD
players (even different brands), and branch circuits. The only thing I
don't like about the branch we're on is it's also powering the fluorescent
room lights (which are OFF during a show).

One other possibility is that the entire firing network is acting like a big
antenna, sucking up 60Hz, and back-feeding the CD output. But again,
there's no visible AC superimposed on the signals to the F1 or the Aquilla,
either between their signal ground and the signal, or between earth ground
and their signal.

And don't forget -- the Aquilla is physically on the same time code _wire_
as the FireOne. It sees the code just fine, and is working on the same
circuit as the CDs.
There CAN be an electrical ground at the Aquilla box. The Aquilla can
operate either on standby battery power or AC, and the performance of the
system, et. al., does not change.

We wrung out a potload of possibilities. The installation has YAG and gas
lasers, too. We moved all the audio equipment physically distant from the
argon/krypton and HeNe lasers, because they tend to broadcast in the .5 to 1
meter frequency range. But they're well-shielded, and doing that didn't
change the situation. The YAG projectors are external to the building, and
remote, so we didn't do anything with them.

LLoyd




.

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